This invention relates to a deflection controlled roll.
In a deflection controlled roll disclosed in West German Pat. No. 31 28 140, a longitudinal chamber enclosed by longitudinal and transverse seals extends over substantially the entire length of a rotable cylinder between two bearings which rotatably support the cylinder on a crosshead. On the side of the roll gap or nip, the pressure liquid contained in the longitudinal chamber exerts a uniform pressure against the inner surface of the cylinder. This pressure is absorbed by the crosshead, which accordingly flexes between the bearings. The bearings are disposed at the ends of the cylinder and constitute between the cylinder and the crosshead a connection fixed in the radial direction. The spaced support by the bearings is the reason for the distance between the crosshead and the inner surface of the cylinder.
Deflection controlled rolls may have lengths of up to 10 m when used, for example, in the paper industry. The maximum radial deflection on the outer side of a bending crosshead may be as much as 30 mm. The distance between the crosshead and the inner surface of the cylinder in the center must be at least as large as this maximum possible deflection.
In transverse planes longitudinally spaced from the center of the roll, the angles between the crosshead and the cylinder (which is not affected by the bend) may increase considerably upon large deflections of the crosshead's center portion. The seals which limit the longitudinal chamber must, of course, remain tight even during such displacements, as otherwise the operating pressure in the longitudinal chamber would collapse.
German Pat. No. 31 28 140 discloses a transverse seal formed as a gap seal, in which a predetermined spacing between the faces at the gap is maintained by a special antifriction bearing formed as part of the seal and bracing the parts defining the gap against one another. In addition, displacements between the crosshead and the cylinder are compensated by mobility of the various parts. In this transverse seal, the bearing has a large diameter and must be very precisely manufactured and fitted. The construction of the seal is accordingly rather costly and enters into consideration primarily in special cases.
Generally, the transverse seals in the above-described deflection controlled rolls are formed as sliding ring seals. German Pat. No. 10 26 609 schematically shows a radial sliding ring seal disposed in a radial groove in a crosshead. However, in practice a transverse seal is usually designed as an axial sliding ring seal having a radial sliding face which abuts in the axial direction against a ring provided in the vicinity of one of the bearings. Sliding ring seals can follow radial displacements of the crosshead and of the inner surface of the cylinder. If misalignments occur, as in the case of large deflections of the crosshead relative to the cylinder, the sliding rings, being guided in the crosshead, are carried along and tilted to a degree determined by the deflection of the crosshead. The result of this tilting is that only the edges of the sliding rings contact the counter-surfaces. This edge-wise contact leads to a great increase in the pressure per unit surface area in the contact zones and to correspondingly increased wear, which may greatly reduce the life of the seal.
In a roll disclosed in German Pat. No. 31 28 140, a longitudinal chamber extends over the full length of the cylinder between the bearings at the ends of the roll. The transverse seals are accordingly arranged directly next to respective bearings on the inner sides thereof. However, the above-described problem occurs not only with these transverse seals, but also when a plurality of longitudinal chambers are disposed one after the other in the axial direction, as in the case of a roll disclosed in German Pat. No. 31 28 722.
An object of the present invention is to provide an improved roll of the above-described type. A more particular object of the present invention is to provide such a roll in which the life of the transverse seals is not decreased by the deflections of the crosshead.